A conventional belt-type clutch mechanism is known that transmits mechanical power by bringing a flat belt into contact with the outer peripheral frictional surface of a rotating member by applying belt tension, and that interrupts the power transmission by bringing the belt out of contact with the frictional surface by slackening the tension.
When such a clutch mechanism interrupts mechanical power, the rotating member idles. While the power is interrupted, the frictional surface of the rotating member and the flat belt would keep slipping on each other. Therefore, in order to keep the durability of the clutch mechanism from decreasing due to friction, the mechanism includes a means for biasing the flat belt radially outward to bring it out of contact with the frictional surface of the rotating member.
As a known biasing means of such a type (for example, refer to Patent Document 1), iron as a magnetic material is kneaded into the rubber layer of a flat belt, and a magnet is spaced outward from the frictional surface of a rotating member radially of the member. When mechanical power is interrupted, the magnetic force of the magnet brings the flat belt out of contact with the frictional surface, keeping the durability from decreasing due to friction.
Flat belts for magnetic flaw detection are known (for example, refer to Patent Document 2). Each of these belts includes one or two rubber layers in which 150-300 parts by weight of magnetic material (magnetic powder of ferrite or the like) for 100 parts by weight of rubber matrix are mixed. One of the belts further includes a tension-resistant layer, and two such rubber layers are laid on the upper and lower sides of the tension-resistant layer. Another of the belts further includes two tension-resistant layers, which are laid on the upper and lower sides of such a rubber layer. Still another of the belts further includes a tension-resistant layer, and such a rubber layer is laid on the tension-resistant layer.
So, it is conceivable to use in the clutch mechanism disclosed in Patent Document 1 the flat belt disclosed in Patent Document 2.